Just for reference:
The S50 US 3 litre cams will fit both the M50 and M52 engine
The S52 US 3.2 litre cams won't fit the M50, but will fit the M52 engine.
The M50 325 and M52 323/328 heads are the same.
It's the cam carrier that won't allow the S52 cams to fit the M50 325 head. The carriers can be changed, but obviously adds to the cost
As far as I know, the Hartge and Alpina cams are the same as Schrick cams.
Kent cams will be reground standard units